Federal immigration officers drive cars without license plates (chicago.suntimes.com)

My understanding is that all federal vehicles that aren't assigned for use of the President or heads of executive departments must have a license plate when operating on state roads.

Pulling over vehicles without plates seems like a reasonable method for local police forces to stop ICE within their jurisdiction. Why isn't this happening?

If this was scaled up to the entire fleet, I imagine several vans would be stolen everyday. Car thieves love this one weird trick..